A transducer of this type is generally disclosed in German patent application, No. 38 24 799.
It is required in such transducers that moisture is prevented from entering the interior of the transducer, so that the cemented piezoceramic plate and the associated electronic component parts and electrical connections will not be damaged. In addition, mechanical damping must not be impaired. More particularly, it is imperative that a transducer of this type is sealed against moisture even if it is subjected to the action of a steam-jet cleaner.
The previously used transducers of the type satisfied these requirements only insufficiently.
Therefore, an object of the present invention is to provide a generic transducer having an improved seal behavior with respect to extreme pressure and temperature.
Thus, the basic principle of the present invention is that a chamber is provided within the surface to be sealed which is relieved from pressure. Naturally, the surface of the projections is smaller than the total surface of the plug so that a larger surface pressure can be provided without impairing the mounting of the plug into the housing. This increased surface pressure in proximity to the projections with respect to the inner wall of the housing contributes to an improved sealing of the housing interior relative to the pressurized hot steam.
Because it is desirable that the diaphragm retainer is accessible to the environment and, thus, is exposed to moisture, in a preferred embodiment of the present invention pressure relief is also effected by the radial bores extending to the outside surface of the diaphragm retainer. Moisture under pressure is drawn outwardly through the radial bore and the apertures so that the adjacent surface of the diaphragm retainer is protected against moisture.
According to a preferred aspect of the present invention, the radial bore and the aperture terminate into the same chamber so that evacuation can be effected from the outside through the two openings up to the surface of the diaphragm retainer.
The sealing behavior is further improved and, additionally, a displacement of the diaphragm retainer in the longitudinal direction of the plug is prevented mechanically.
According to still another preferred aspect of the present invention, the sealing effect can be increased by the provision of a plurality of chambers. In addition, mounting of the plug is thereby simplified because a plurality of chambers are formed over the periphery of the plug. The walls of the chambers exert an increased surface pressure on the inside wall of the housing but, simultaneously, permit a comparatively simple mounting of the plug into the housing interior.
To minimize the influence of moisture on both the outside surface of the plug and the inside surface of the diaphragm retainer, radial bores terminate into a chamber.
Preferably circumferential projections are received and locked in the grooves of the diaphragm retainer.
The ventilation effect, which additionally aids in removing the fluid that entered and decreasing a pressure that developed in the chamber, can be increased by offsetting the radial bores and the apertures terminating into the first chamber. To this end, the boundary surfaces between the environment and the chamber or the outside surface of the diaphragm retainer are increased, and the offset positioning of apertures and radial bores virtually prevents the direct ingress of moisture. It is of course favorable that at least one of the bores extends vertically downwardly in the mounted condition to facilitate the removal of moisture.
The plug, which is formed of an elastic material such as silicone, can also be used for the elastic accommodation of a printed circuit board. The plug and the features indicated hereinabove will aid in protecting the housing chamber against moisture and other environmental influences.